1 files changed, 42 insertions, 0 deletions
diff --git a/user/primes.c b/user/primes.c
new file mode 100644
index 0000000..49c545a
--- /dev/null
+++ b/user/primes.c
@@ -0,0 +1,42 @@
+#include "user.h"
+
+void _start(void)
+{
+    put("primes up to N, enter N (empty line quits)\n");
+    char line[32];
+    for (;;)
+    {
+        put("> ");
+        int length = read_line(line, 32);
+        put("\n");
+        if (length == 0)
+            break;
+
+        long limit = 0;
+        for (int position = 0; position < length; position++)
+            if (line[position] >= '0' && line[position] <= '9')
+                limit = limit * 10 + (line[position] - '0');
+
+        int count = 0;
+        for (long candidate = 2; candidate <= limit; candidate++)
+        {
+            int prime = 1;
+            for (long divisor = 2; divisor * divisor <= candidate; divisor++)
+                if (candidate % divisor == 0)
+                {
+                    prime = 0;
+                    break;
+                }
+            if (prime)
+            {
+                put_int(candidate);
+                put(" ");
+                count++;
+            }
+        }
+        put("\n");
+        put_int(count);
+        put(" primes\n");
+    }
+    sys_exit(0);
+}